The ultimate goal of the program is to elucidate the biological process of aging in exocrine secretory cells. The immediate objectives of the proposed study are to determine whether or not age-related changes occur in these cells with respect to the ability or potential to form secretory products. Using the acinar cells of the parotid salivary gland of rats as a model system, studies will be done to determine whether or not there are changes in synthesis, processing and packaging of secretory proteins with increasing age, and whether or not these changes accompany structural alterations in the intracellular organelles concerned with these processes. These studies will be done by utilizing the techniques of amino acid incorporation analyses, electron microscopic radioautography and cytochemistry as well as routine electron microscopy.